The present invention relates to deicing agents and their methods of use. More specifically, the present invention relates to a combination of spent sulfite liquor, chloride salts of alkali metals or alkaline earth metals as deicing agents, and one or more additives which reduce the corrosive tendencies of the deicing agent. The amount of corrosion damage normally encountered in road deicing is reduced by the present invention.
It is generally recognized that the needs of business, industry, and the general public demand that traffic be kept moving with reasonable safety in the face of snow or ice. Reliance on mechanical means of snow or ice removal alone, however, is insufficient to ensure the safe and efficient movement of traffic. At present the only feasible means for "bare pavement" maintenance is by the use of deicing salts. Rock salt or sodium chloride is the primary chemical used for deicing primarily because of its low cost, ease of transportation, and readily dispersible form.
The cost of deicing salt is deceptively low given the unassumed cost of corrosion to metal guardrails, bridge supports, metal concrete reinforcing rods and automobiles. The estimated cost of upgrading deficient bridges in the United States alone approaches $50 billion dollars. Chemical Marketing Reporter, Aug. 27, 1984.
Other chemicals have been used in place of alkali metal or alkaline earth metal chlorides, e.g. mixtures of urea and calcium formate with a formamide spray, calcium magnesium acetate, metal sulfates, phosphates, nitrates, amides, alcohols, long-chain amines, and sodium dichromate. None of these chemicals have gained wide-spread popularity due to their high cost, low effectiveness and/or high degree of toxicity. Chlorides remain the standard notwithstanding their corrosivity.
Some work has been performed on reducing the corrosivity of alkaline earth metal chloride salts applied to road surfaces by utilizing lignosulfonate as one component of a deicing agent. Japanese Pat. No. 51-12310 discloses the use of a three-part mixture of calcium chloride, a small amount of calcium lignosulfonate and calcium hydroxide as a dust-control or anti-freezing agent. A 1 to 3 percent (dry weight) mixture of calcium lignosulfonate to calcium chloride (lignosulfonate:calcium chloride ratio up to 1:35) was tested, with essentially no corrosion inhibition. Some rust preventing effect was observed when calcium hydroxide was combined with calcium chloride. When both calcium lignosulfonate and calcium hydroxide were mixed with calcium chloride, however, a greater rust-preventing effect was demonstrated and the Japanese patent is specifically directed to the combination that contains both lignosulfonate and calcium hydroxide in combination with calcium chloride. Each of the combinations disclosed in the Japanese patent contains 1-5% calcium lignosulfonate and also contains at least as much calcium hydroxide. Tests have demonstrated that those solutions have a pH of about 10 or higher.
Spent sulfite liquor has been used for many years as a dust-control agent applied directly to dirt or gravel roads. Use of chloride salts of alkaline earth metals to prevent dusting is also known. Freight considerations often determine whether spent sulfite liquor or chloride salts are used in any particular locality.
The prior art deicing agents such as sodium chloride, calcium chloride, magnesium chloride, or rock salt, ultimately cost the consuming public far more in corrosion damage than the initial material cost would indicate. Accordingly, a composition which alleviates the corrosion problem would be a highly desirable advance in the art of deicing agents for road surfaces.
Recently disclosed and commercialized under U.S. Pat. No. 4,668,416 is a deicing composition of one or more chloride salts and a lignosulfonate salt. The commercial composition comprises chlorides of sodium and magnesium in addition to lignosulfonate. The lignosulfonate additive is available under the name PCI.RTM. and acts to decrease the corrosion rate of the mixture at pH values of about 4.5 to about 8.5. Notwithstanding the beneficial decrease in corrosion achieved with the '416 patent, it would be desirable to reduce the corrosive action of deicing agents even further.